If you are using products such as Cofense PhishMe , FriendlyPhishing or Knowbe4 as Phish testing software in your organisation then these test’s will get blocked in Mimecast. These organisations will give you a list of IP Addresses e.g for Cofense PhishMe ( 18.104.22.168, 22.214.171.124, 126.96.36.199 and 188.8.131.52 ) which you will need to whitelist through Mimecast
Login to the portal and choose Policies then Permitted Senders
Create a new policy with the below options :
Trackback from your site.